Robert Y. Thornton (January 28, 1910 – November 29, 2003) was an American attorney, politician, and jurist in the U.S. state of Oregon. A Democrat, he was the second-longest serving Oregon Attorney General in the state's history, holding that office from 1953 to 1969. His 16-year tenure was second only to Republican Isaac Homer Van Winkle, who bested him by seven years, serving from 1920 to 1943. Thornton was the Democratic nominee for Oregon Governor in 1962, losing in the general election to incumbent Mark Hatfield.